Motor control



July 10, 1945. E. L. SCHWARZ MOTOR CONTROL Filed Jan. 10,

1942 2 Sheets-Sheet 1 @h P Q MQ we [mi/E27 far fewsr 1 Sal/M422 July 10, 1945.

E. L. SCHWARZ MOTOR CONTROL Filed Jan. 10, 1942 2 Sheets-Sheet 2 N 2w RN 5 NQ mi 24 Patented July 1945 MOTOR CONTROL Ernst L. Schwarz, Chicago, 111., assignor to Armour Research Foundation, Chicago, 111., a corporation of Illinois Application January 10, 1942, Serial No. 426,277

1 Claim.

This invention relates to an electric motor speed controlling system, and more particularly to a speed controlling system for a three phase induction motor of the wound rotor type.

The present invention relates primarily to motors which are employed for driving large fans, or other loads, arranged to run at different speeds, and which have the characteristic that the torquerequired decreases faster than the square of the speed reduction. Motors for driving fans should be capable of operating over a wide range of speeds without having too great a difference between the torque developed and the torque required. The reason for this is that it is diflicult to obtain low speed without great loss of eificiency when the speed is controlled by a variable resistance means in the rotor circuit.

One of the important features and objects of the present invention is to provide a three phase induction motor of the wound rotor type in which provision is made for varying the rotor resistance and simultaneously varying the connection of the two part windings of each phase of the stator in accordance with a predetermined schedule.

It is old in the art to provide switching means to connect the two part windings of each phase of the stator, either in parallel or in series, but these have always been employed in a constant speed motor or as a starting means to bring the motor up to speed. The prior art has not provided any system, however, in which the part windings of the stator have their connections changed and at the same time causing a change in the resistance in the wound rotor. By making this simultaneous change in accordance with a predetermined schedule, an extremely eflicient speed control can be obtained for a three phase induction motor which is employed for driving a fan, or other load which has the above mentioned characteristics.

It is an object of the present invention to provide an electric motor speed controlling system having the above referred to characteristics.

It is a further object of the present invention to provide a three phase induction motor of the type having two part windings in each phase of the stator and a wound rotor with switching and control means for simultaneously changing the electrical connections of the part windings of the stator and the resistance of the rotor.

Another object of the present invention is to provide a novel method and means of controlling the speed of an alternating current electric machine.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claim. My invention itself, however, both as to its organization, manner of construction, and method of operation, together with further objects and advantages thereof, may bestv be' understood by reference to the following description taken in connection with the accompanying drawings, in which:

Figure 1 is a schematic wiring diagram of an electric control system for a. three phase wound rotor induction motor embodying the novel features of the present invention; and

Figure 2 is a schematic wiring diagram showing a second embodiment of my invention.

In Figure 1 of the drawings; I have illustrated a three phase wound rotary induction motor having a stator S and a rotor R, The stator S is a three phase stator with two part windings in each phase, as is indicated at Ill, ll, [2, l3, I4 and I5.

These six winding-s'are arranged to be connected in a wide variety of manners to a three phase source of power supplied through conductors Hi,

l1 and I8. Each end of each of the stator windings in to l5, inclusive, are connected to contactor shoes Is to 36, inclusive. As is clearly shown in Figure 1 of the drawings, the outer ends of the windings In, ll, 1'2, l3, l4 and i5 are connected to contactor shoes H, 21', I93, 25, 20 and 26, respectively, while the inner ends of these same windings are connected to contactor shoes 2!, 3'0, 22, 28., 23 and 29, respectively.

The rotor R is shown as comprising three windings 3|, 32 and 3.3, connected in star. It is to be understood, however, that the rotor windings may be connected in any other manner, such as connected in delta, without departing from the spirit and scope oi the present invention. The rotor is connected through slip rings 34, 35 and 35 to a resistance unit Z. This resistance unit Z has three resistance elements 31, 38, and 39, which are connected together at one end by conductor 40. Resistance elements 38 and 39 are connected a shown for engagement with slip rings 35 and 36. Resistance element 31, however, is connected to a contactor shoe M of the controller C, while slip ring 34 is connected through a suitable sliding shoe (not shown) to contactor shoe 42 of controller C. The slip ring ends of resistance elements 38 and 39 are connected to contactor shoes 43 and 44, respectively. An intermediate point 45, on resistance element 31, is connected to contactor shoe 48, respectively, on controller C. Two intermediate points 49 and 50 on resistance element 38 are connected to contactor shoes and 52 on controller C. One intermediate point 53 on resistance element 39 is connected to contactor shoe 54 on controller C. The slip ring end of resistance element 31, in addition to 39 are connected as at 46 to contactor shoe 41 on controller C.

The three phase power supply lines I6, I1, I8, have their respective individual conductors connected to contactor shoes 56, 51 and 58, on controller C.

The controller C may be of any suitable variety well known to'those skilled in the art, such as a. cylindrical controller, or a flat sliding plate type controller, in which a series of contactor bars are mounted and arranged to be engaged by one or more of the sliding contactor shoes through a series of difierent positions. The controller C as shown, is a controller having ten positions asindicated by the broken lines, and whose positions are indicated by the Roman numerals. Three contactor bars 59, 00 and BI are provided on the controller C for progressive engagement with the contactor shoes 56, 51 and 58, respectively. It will be observed that the contactor bars 59 to SI extend across all ten positions of the controller C. The contactor bars 59, 60 and 8| are electrically connected by cross connections 62, 93 and 64, to the contactor bars 85, 68 and 61, which also extend across all ten positions of the controller C, The contactor bars 65, 66 and 61 are arranged to be engaged by the contactor shoes I9, 20 and 2I in all ten positions of the controller C and thus for all ten operating positions of the controller C, power is supplied through the contactor shoes I9, 20 and 2I to the outer end of winding I2, the outer end of winding I4 and the outer end of winding I0.

Two groups of contactor bars areprovided for contactor shoes .22 to 30, inclusive. The first group of contactor bars 88 to 16 extend across the first five positions of the controller C, and they are arranged to be engaged by contactor shoes 22 to 30, respectively. The second group of contactor bars 11 to 85 are also arranged to be engaged by contactor shoes 22 to 30, respectively, and extend across the last five positions of the controller C, or more particularly, extend across positions VI to X.

The contactor bars 68 to 19 are connected in such a manner as to cause the two part windings in each phase of the stator S to be connected in series, and at the same time the phases are connected in star. This is accomplished by connecting contactor bar 58 with contactor bar 1| as at 88; contactor bar 69 with 13 as at 81; contactor bar 10 with 13 as at 88; and, contactor bars 14, 15 and 18 together as at 89.

The part windings I0 to I5 in the stator S are arranged to be connected in parallel in each phase by the contactor bars 11 to 85. For this purpose .contactor bar is connected to contactor bar 65 through the cross connection 90; contactor bar BI is connected to bar 86 through the cross connection 9I; contactor bar 82 is connected to bar 61 through cross connection 92; contactor bar 83 is connected to bar 11 through cross connection 93; contactor bar 84 is connected to bar 18 through cross connection 94; contactor bar 85 is connected to bar 19 through cross connection 95; and, contactor bars 85, 84 and 83 are also connected to each other through cross connections 96 and 91.

The rotor R is arranged for operation as a three phase rotor and also as a single phase rotor by opening one phase. Contactor bars 98 and 99 on controller C extend across positions V to X and determine whether the rotor is to operate as a single phase rotor or as a three phase rotor. More particularly. the contactor bars 98 and 99 are arranged to be engaged by the contactor shoes 42 and 4|, respectively, when the controller C is in any one of its last six positions.

The remaining contactor bars I00 to I 08 on the controller C are arranged to connect varying amounts of resistance into the rotor circuit. Contactor bar I00 extends across positions II to X, inclusive; contactor bar IOI extends across positions III to X, inclusive; contactor bar I02 extends across positions V to X, inclusive; contactor bar I03 extends across position IV only; contactor bar I04, which is arranged to be engaged by the same contactor shoe, namely, contactor shoe 5|, as is contactor bar I03, extends across positions VIII to X, inclusive; contactor bar I05 extends across positions VI and VII; contactor bar I06 extends across positions IX and X, and is arranged to be engaged by the same contactor shoe 43 as bar I05; contactor bar I01 extends across position VII only; contactor bar I08 extends across positions IX and X, and is arranged to be engaged by the same contactor shoe 55 as bar I01; contactor bar I09 extends across position X only; and contactor bar IIO extends across positions II to X, inclusive.

Contactor bars 98, 99, I00, IOI, I02, I04, I06,

I08, I09 and H0 are all interconnected by the cross connections I00, III, H2, H3, H4, H5, H6, H1, and H8.

Contactor bar I03 is connected to contactor bar IOI by a cross connection II9. Contactor bars I02, I05 and I01 are connected together by cross connections I20 and I2 I.

, By moving controller C through its range of positions, a wide variety of motor speeds may be obtained with less power and greater elliciency than anything heretofore known by me.

For purposes of illustration and by way of example, a table is given below for a motor arrangement of the above described type, but in which a larger number of rotor resistance steps were used than is shown in the illustrated embodiment in the drawings. More specifically, on the resistance Z, and for purposes of simplicity, the drawings illustrate a current in which some of the steps on the rotor resistance unit were eliminated to avoid an excessive number of lines on the drawings, The circuit of the drawings employs resistor steps 1, 5, 8, 9, 10, 11, 12 and 13 of the tablewhich is nowgiven by way of example:

I35 and I36 to a resistance unit forvariable-resistor Z". This resistor Z has three resistance Table Iv I II 111 A Part windings in parallel Part windings in series Resistor steps Three rotor phases Three rotor phases One rotor phase disconconnected connected necte R. P. M. "Watts P. F. R. P. M. 5 Watts P. F. R. I; M. Watts P. F.

530 800- an 240 44 164 200 44 560 800- 35 v 270 280 52 174 200 44 590 900 39 330 320 55 213 220 46 635 1, 000 .42 360 360 60 240 240 .48 6B5 1, 100v .45 400 420 .65 270 270' .52 730 1,200 .48 j 450 480 68 310' 300 .54 790 1-, 300 500' 580 72 360 360 58 850 1, 40(1 1 53 545 l 640 76. 400 400 61 890 1, 600 57 590 740 77 445 44G 59 940 l, 700 .59 650' 860 .80. 500 490' 59 in series a speed of 590 R. P. M. may be obtained with the expenditure of only 740 watts, a net savings of 160 watts, and at the same time a greatly improved power factor is obtained, namey; a power factor of .77, and furthermore, only a fractional part of the ohmic resistance is, required.

Figure 2 of the drawings illustrates a second embodiment of the invention wherein the. stator of a wound rotor induction motor is arranged to be connected either in delta or in star, while the resistance in the rotor circuit is simultaneously being changed.

The motor illustrated in Figure 2 is a. three phase wound rotor induction motor having a stator S, a rotor R and a variable resistor Z. The stator S is a three phase stator which is provided with coil parts I22, I23 and I24. These coil parts are arranged to be connected in such a manner that the stator is either a delta wound stator or a star wound stator. The coil arts are arranged to be connected as desired through the medium of a controller C; which ma be of any suitable variety well known to those skilled in the art, such as a cylindrical controller, in which a series of conductor bars are mounted and arranged to be engaged by a series of sliding contactor shoes through a series of different positions.

Each end of each coil part I22, I23 and I24 is connected to an associated contactor shoe on the controller C. More particularly, coil part I22 has its opposite ends connected to contactor shoes I21 and I30; coil part I23 has its opposite ends connected to contactor shoes I25 and I28; and, coil par-t I24 has its opposite ends connected to contactor shoes I26 and I29.

The rotor R is shown as comprising three windings I3I, I32 and I33, connected in star. It is to be understood, however, that the rotor windings may be connected in any other manner, such as connected in delta, without departing from the spirit and scope of the invention. The rotor R is connected through slip rings I34,

elements I31, I38 and I39, which are connected together at one end b conductor I 46 Resistance elements I38 and I39 are connected as shown, with slip rings I35 and I 36. Resistance element I31, however, is connected to a contactor shoe M2 on controller C; while slip ring I 34 is connected to a contactor shoe- I II on controller C. The slip ring end of resistance element I31 is also connected to a contactor shoe I51. The slip ring ends of resistance elements I38- and I39 are connected to contactor shoes I56 and ['55, respectively. Four intermediate points I58, 159', I66 and I6I on resistance element. I31 are connected respectively to contactor shoes; I45, I48, I5I and I54 011 controller C. Four intermediate points I62, I63, I64 and I65 on resistance element I38 are connected respectively to. contactor shoes I44, I41, I56 and I53 on controller C. Four intermediate points I66, I61, I68 and I69 on resistance element I39 are connected; respectively to contactor shoes I43, I46, I49 and I52 on controller C.

Three phase power is supplied to the motor through conductors I18, HI and I12 which are connected respectively to contactor shoes I13, I14 and I15 on controller C.

The controller C and the arrangement of the conductor bars thereon which are arranged to be engaged by the contactor shoes above referred to will now be described. The controller C as shown, is a controller having ten positions as indicated by the broken lines, and whose positions are indicated by the Roman numerals. Three conductor bars I16, I11 and I18 are provided for progressive engagement with the contactor shoes I13, I14 and I15, respectively. It will be observed that the conductor bars I16, I11 and I18, which are associated with the source of power, extend across all ten positions of the controller C. Another group of contactor bars I19, I and I8I, which are positioned to be engaged by contactor shoes I25, I26 and I21, also extend across all ten positions of the controller C. These contactor bars I19, I80 and I8I are connected by cross connections I82, I83 and I84 to contactor bars I16, I11 and I18.

Means for connecting the coils parts I22, I23 and I24 of stator S in star is provided by three conductor bars I85, I86 and I81, which are connected together by cross connections I88 and I89. It will be observed that the bars I86 and I 81 extend across only the first two positions of the controller C and for that reason it will be understood that the stator S is connected in star only in the first two positions of the controller C. Three additional conductor bars I90, I9l and I92 are also arranged to be engaged by the same con tactor shoes, I28, I29 and I30, as were bars I85, I88 and I81. The bars I90, I9I and I92 extend across positions IIIto X of the controller C. A cross connection I93 between bars I80 and I92, a cross connection I94 between bars I19 and ISI, and a cross connection I95 between bars I8I and I99 cause the stator S to be connected in delta when the controller C is in any one of its last eight positions.

The rotor is arranged to have one phase opened in the first position of the controller C and to cause varying amounts of resistance to be placed in the rotor circuit through each of the succeeding positions of the controller C. To this end, seventeen contactor bars I96 to 2I2, inclusive, are provided on the controller C, and are arranged to extend across the positions as indicated in Figure 2. The first two bars of this group, namely bars I96 and I91, are the bars which determine whether the rotor has one phase opened or not, and are arranged to be engaged by contactor shoes MI and I42. The bars I96 and I9! are connected together by a cross connection 2I3. The remaining bars I98 to 2I2, inclusive, are arranged to be engaged by contactor shoes I43 to I51, respectively, and are all connected together by cross connections 2I4 to 221, as shown.

From the above description it will be apparent that when the controller is moved to its first position, the stator S is connected in star and the rotor has one phase opened while resistance is connected in the remaining portion of the rotor circuit. When the controller C' is moved to position II, the stator S is still connected in star, but the rotor isnow connected for three phase operation and all of the resistance of the vari- 'able resistor Z is connected in the circuit of the rotor R. When the controller C is moved to position III, the stator is switched from a star arrangement to a delta arrangement and the rotor which is now operating as a three phase rotor still has all of the resistance of variable resistance unit Z connected in its circuit.

When the controller C is moved to position IV, the stator is still connected in delta but a portion of the resistance which was in the rotor circuit has now been shorted out by contactor bars I98, I99 and 200, moving into engagement with contactor shoes I43, I44 and I45. As each succeeding position of the controller C is reached, additional resistance is shorted out of the rotor circuit until position X is reached, at which time all of the resistance is shorted out.

While no illustrated example by way of a table is given for this embodiment of the invention, it will be apparent to those skilled in the art that equivalent beneficial results may be obtained with the arrangement shown in Figure 2.

While I have shown particular embodiments or my invention, it will, of course, be understood that I do not wish to be limited thereto, since many modifications may be made, and I, therefore, contemplate by the appended claim to cover all such modifications as fall within the true spirit and scope of my invention.

I claim as my invention:

In a motor control system, the combination comprising a motor having a poly-phase stator with at least two part windings in each phase, and a poly-phase wound rotor, variable resistance means connected to said rotor and forming a rotor circuit, and a controller arranged to be selectively moved through a plurality of positions representing different motor speeds, said controller having means thereon for connecting the part windings in each stator phase in series throughout a first predetermined number of positions and then in parallel throughout a second predetermined number of positions, said controller also having means thereon for maintaining one phase of said rotor circuit open throughout a first part of said first predetermined number of positions while changing the resistance value for each position of said first part of said first predetermined number of positions, then connecting the rotor circuit for poly-phase operation throughout the remaining positions and varying the resistance in the rotor circuit in a predetermined manner for each said remaining positions.

ERNST L. SCHWARZ. 

